As for a capacitor having high capacitance used in various electronic devices, a solid electrolytic capacitor is known wherein an oxide dielectric film layer, a semiconductor layer and an electrode layer are formed sequentially on an electric conductor and sealed with resin mold jacketing.
A solid electrolytic capacitor is produced by sealing a solid electrolytic capacitor element in which an aluminum foil having fine pores in the surface layer or a tantalum powder sintered body having fine pores in the inside is used as one electrode (electric conductor) and which comprises a dielectric layer formed on the surface layer of the electrode, the other electrode (usually a semiconductor layer) provided on the dielectric layer, and an electrode layer stacked on the other electrode. In comparison among capacitors using electric conductors having the same volume, the smaller the size of the fine pores of the electric conductor and the larger the number of the pores, the larger the surface area of the electric conductor inside and the larger the capacitance of the capacitor produced from the electric conductor can be.
Recently a solid electrolytic capacitor is required to have low ESR (equivalent series resistance) and therefore an electrically conducting polymer is used in preference as an inside semiconductor layer. Such a semiconductor layer is formed by chemical polymerization or electrolytic polymerization.
Electrolytic polymerization is generally conducted using an electric conductor on the surface of which a dielectric layer is formed as an anode and a negative electrode plate placed in an electrolytic solution as a cathode with direct current, but a method using alternate current at the time of electrolytic polymerization has also been reported (JP-A-H02-299213: Patent Document 1). However, according to this method, a large amount of polymer is also formed on a cathode, which may lead to short circuit.
Patent Document 1: JP-A-H02-299213